The present invention relates generally to evaluation and verifier systems. More particularly, the invention relates to methods of processing 2-dimensional (2D) image data to evaluate the relative print quality of a data carrying symbol. Exemplary data carrying symbols include 1D and 2D bar code symbols, which may be contained or embedded within collected image data.
The advent of bar code symbols, including 1D and 2D symbologies, has lead to a revolutionary change in the way products, packages, shipments, and the like, are handled, inventoried, and tracked. At the present time virtually every product made that is individually packaged, and or shipped from a first location to a second, has a bar code symbol associated with it. The development and acceptance of 2D bar code symbologies, such as PDF-417, Data Matrix, and others, has further expanded the use of bar code technology into new and diverse marketsxe2x80x94in many countries around the world.
As always, there is a need to provide for an efficient and dependable evaluation of the (print) quality of 1D and 2D bar code symbols, especially as they are printed or otherwise disposed upon a substrate. Such verification may be performed on-line, say as a printing web is running, or alternately off-line, by examining one or more recently printed symbols. It should be noted that a large number of varied printing techniques are employed to apply bar code indicia to packages, containers, and other substrates. In all cases there is a well established need to verify the quality of the resulting indicia/symbol. Considerations such as the decodability, symbol contrast, first read rate (FRR), substitution error rate (SER), and others, are of critical importance when evaluating the quality of bar code indicia.
Proper quality verification of certain types of data carrying graphical symbols, including stacked and matrix 2-dimensional bar code symbols, provides an especially difficult challenge. This is particularly true when analyzing certain parameters that are derived from measurements of a scan reflectance profile (SRP) signal, or equivalent data sets, which will be described by way of the preferred embodiments disclosed herein. A guideline from the American National Standards Institute (ANSI) titled xe2x80x9cBar Code Print Quality Guidelinexe2x80x9d defines several such parameters. This evaluation guideline (ANSI X3.182-1990), which is well known to skilled persons, is hereby incorporated herein by reference. Although the ANSI print quality guideline is generally associated with 1-dimensional bar code symbols, it may certainly be extended to 2-D symbols as well. In fact, the quality measurement specifications for certain symbologies, such as PDF417, specifically reference the ANSI specification. Importantly, the ANSI specification provides several measurement methodologies (see section 4) and includes the definition of a number of xe2x80x98figures of meritxe2x80x99 or xe2x80x98quality parametersxe2x80x99, which can be determined from one or more digitized and stored scan reflectance profile signals.
A major problem when scanning and verifying high density bar code symbols, especially 2D symbols such as a PDF417, is the need to take a plurality of scans across the symbol using desired scan paths that are substantially orthogonal to the height of elements (such as start bars, stop bars, as well as spaces and or bars of particular stacked row characters). This difficulty of providing complete or substantial verification of 2D symbols is acknowledged in the specifications of 2D symbologies. For example, when considering the print quality evaluation of PDF417 bar coded symbols, known specifications recommend verification only using the start and stop elements, which can easily be scanned in a manual or automated manner. A primary problem with full verification of a 2D symbol is the need to scan or otherwise capture an image of a 2D symbol at a specific (orthogonal) angle. As such, when collecting an image via an imaging array (e.g., a CCD imaging device) or a plurality of substantially parallel and equi-spaced scans taken along a height of the symbol, the symbol is most preferably xe2x80x98imagedxe2x80x99 at a specific (non-arbitrary) angle. When this is the case, each scan taken may then be directly analyzed to assess the print quality of that portion of the scanned symbol.
When scanning and data collection occur at a non-orthogonal angle, which may be termed an xe2x80x98arbitrary anglexe2x80x99, direct analysis is generally not possible. Further, a digitized image containing a 1D or 2D bar code oriented at some arbitrary angle, is not trivial to analyze to make a thorough print quality assessment. It is for this reason certain specifications (e.g., the PDF417 AIM Spec) recommend just a partial evaluation of a 2D graphical symbol via an analysis of portions of an SRP signal corresponding to only the start and stop elements. This does not provide for a very good indication of the quality of the entire indicia!
Therefore, skilled persons will recognize a need for methods and means to facilitate and or support ANSI level quality verification and evaluation (and equivalents thereof) of all or selected portions of 1D and 2D bar code symbolsxe2x80x94even when scanned or imaged at some arbitrary angle. Further, such evaluation must be provided even when the symbol or indicia of interest is contained within other printed textual and graphical information, that is imaged, digitized, and stored as a plurality of data values (available, for example, as a 2D raster-type image).
A full understanding of the present invention, including an understanding of a number of capabilities, characteristics, and associated novel features, will result from a careful review of the description and figures of several embodiments provided herein. Attention is called to the fact, however, that the drawings and descriptions are illustrative only. Variations and alternate embodiments are contemplated as being part of the invention, limited only by the scope of the appended claims.
In accordance with the present invention, methods are provided for collecting and or processing a 2-dimensional image, which contains image data of a data carrying graphical symbol, to enable a thorough print quality evaluation of the graphical symbol to be realized. The methods may commence with the collecting of a plurality of data values, with each data value representative of a level of reflectivity of an associated spatial image position within the 2-dimensional image. Once data values are available, the determining of scan paths, which may be termed xe2x80x98virtual scan pathsxe2x80x99 along desired paths, may commence. Importantly, the determined desired paths traverse selected portions of the graphical symbol at a selected and desired orientation. Next, the extracting and or processing a plurality of the data values associated with each determined virtual scan path occurs, wherein each plurality of data values is representative of a digitized virtual scan reflectance profile signal that may be processed to determine and provide at least one figure of merit indicative of the print quality of an imaged data carrying graphical symbol contained within the 2-dimensional image.